Liquid cooling jacket

ABSTRACT

A liquid cooling jacket (J 1 ) transmits heat generated by a CPU ( 101 ) which is installed at a predetermined position to coolant supplied from an external heat transmission fluid supply means and flowing inside of the liquid cooling jacket. The liquid cooling jacket includes a first flow passage (A 1 ) on a side of the heat transmission fluid supply means, a second flow passage group (B 1 ) including a plurality of second flow passages (B 1   a ) branched from the first flow passage (A 1 ), and a third flow passage (C 1 ) installed at downstream side of the plurality of the second flow passages (B 1   a ), and collecting the plurality of the second flow passages (B 1   a ), wherein the CPU ( 101 ) mainly dissipates the heat to the second flow passage group (B 1 ).

FIELD OF THE INVENTION

The present invention relates to a liquid cooling jacket for cooling a heating element such as a CPU.

In recent years, cooling a CPU (Central Processing Unit) (a heating element) becomes more and more important because the heating value of a CPU has been increasing with the improvement of the performance of electronic devices such as a personal computer. Conventionally, a heat sink air-cooling fan has been used to cool a CPU. However, the heat sink air cooling fan has problems of fan noise and cooling limit. Thus, a liquid cooling jacket (also referred to as a water cooling jacket or a liquid cooling module) has been receiving attention as a next generation cooling method.

As for such a technique, Japanese Laid-open Patent Application No. 1988-293865 discloses a liquid cooling jacket incorporating a serpentine metallic tube wherein an inlet and an outlet are provided at ends of the metallic tube (see page 2, line 2 in an upper right column to page 2, line 15 in a lower left column, FIG. 1 and FIG. 2).

DISCLOSURE OF THE INVENTION Problems to be Solved

However, a coolant incurs a large pressure loss when a liquid cooling jacket comprises only one flow passage through which the coolant flows as shown in the patent document. This causes problems that not only a CPU cannot be cooled efficiently, but also the output power of a pump has to be increased to supply the coolant.

In view of the above, the present invention seeks to provide a liquid cooing jacket which is able to cool a heating element such as a CPU efficiently.

Means to Solve the Problems

In order to solve the above problems, there is provided a liquid cooling jacket for transmitting heat generated by a heating element which is installed to a predetermined position, to a heat transmission fluid supplied from an external heat transmission fluid supply means and flowing inside of the liquid cooling jacket, the liquid cooling jacket including a first flow passage on a side of the heat transmission fluid supply means, a second flow passage group consisting of a plurality of second flow passages branched from the first flow passage, a third flow passage installed at downstream side of the plurality of the second flow passages, and collecting the plurality of the second flow passages, wherein the heating element mainly dissipates the heat to the second flow passage group.

In accordance with the liquid cooling jacket, the heat transmission fluid is supplied to the first flow passage from the external heat transmission supply means. Then, the heat transmission fluid flows through the second flow passage group and the third flow passage in sequence. The heat generated by the heating element is mainly dissipated to the second flow passage group and then transmitted to the heat transmission fluid. As a result, the heating element is efficiently cooled.

In the liquid cooling jacket, the second flow passage group consists of the second flow passages branched from the first flow passage, and the plurality of the second flow passages is collected by the third flow passage. In accordance with this configuration, a length of each of the second flow passages is remarkably shorter than that of the second flow passage of the liquid cooling jacket comprising only one serpentine second flow passage. Accordingly, the pressure loss of the heat transmission fluid flowing through the plurality of the second passages is remarkably lower than that of the heat transmission fluid flowing through the long second flow passage. It is also to be noted that the second flow passages adjacent to each other do not have to be completely isolated in the present invention, as shown in second flow passages 5 a, 5 a of a liquid cooling jacket J6 according to a sixth embodiment of the present invention, which is described later (refer to FIG. 26).

In accordance with the liquid cooling jacket, the heat transmission fluid can be supplied and made to flow inside the liquid cooling jacket, and the heating element such as a CPU can be cooled efficiently by using the external heat transmission fluid supply means of which an output power is small (e.g. a pump).

There is also provided a liquid cooling jacket for transmitting heat generated by a heating element which is installed to a predetermined position, to a heat transmission fluid supplied from an external heat transmission fluid supply means and flowing inside of the liquid cooling jacket, the liquid cooling jacket comprising: a first flow passage, a plurality of a second flow passage groups each of which consists of a plurality of second flow passages, and a third flow passage toward downstream in order, wherein the heating element mainly dissipates the heat to the second flow passage groups, and the adjacent second flow passage groups are connected in series via a communication flow passage. In short, this is a liquid cooling jacket wherein a plurality of the second flow passage groups is provided and the plurality of the second flow passage groups is connected in series.

In accordance with this liquid cooling jacket, because the liquid cooling jacket is provided with the plurality of the second flow passage groups connected in series via the communication flow passage, the heat can be exchanged between the plurality of the second flow passages and the heating element.

In the aforementioned liquid cooling jacket, the adjacent second flow passage groups may be disposed side by side, and a lower end of one of the adjacent second flow passage groups and an upper end of the other one of the adjacent second flow passage groups may be on the same side. That is, this is a liquid cooling jacket wherein the adjacent second flow passage groups are disposed side by side, and a lower end of one of the adjacent second flow passage groups and an upper end of the other one of the adjacent second flow passage groups are on the same side.

In accordance with this liquid cooling jacket, the heat transmission fluid meanders through one of the second flow passage groups adjacent in a flowing direction of the heat transmission fluid, the communication flow passage and the other one of the adjacent second flow passage groups. Therefore, when the size of the liquid cooling jacket in a plain view is constant, if the number of the second flow passage groups is increased without changing the number of the second flow passages constituting each of the second passage groups, a cross-sectional area of each of the second flow passages constituting each of the second flow passage groups becomes smaller. Therefore, when a flow rate of the heat transmission fluid flowing through the liquid cooling jacket is constant, if the number of the second flow passage groups is increased, a flow speed of the heat transmission fluid in each of the second flow passages is increased. Thus, thermal conductivity between the liquid cooling jacket and the heat transmission fluid is increased, and thermal resistance of the liquid cooling jacket decreases accordingly.

On the contrary, when the adjacent second flow passage groups are not disposed side by side, but disposed in line in the flowing direction, for example, even if the number of the second flow passage group is increased, a length of each of the second flow passages constituting each of the second flow passage groups becomes shorter, but a cross-sectional area of each of the second flow passages does not become smaller, and thus a flow speed of the heat transmission fluid is not increased either. Therefore, the thermal resistance of the liquid cooling jacket does not decrease.

If the number of the second flow passage groups is even number, the inlet of the liquid cooling jacket for the heat transmission fluid and the outlet thereof can be arranged on the same side. This makes it possible to readily install piping to the liquid cooling jacket.

The aforementioned liquid cooling jackets may further include a tube bundle formed by bundling a plurality of metallic tubes, wherein an inner hole of each of the plurality of metallic tubes is the second flow passage.

In accordance with the liquid cooling jackets, which include the tube bundle formed by bundling the plurality of metallic tubes, the inner holes of each of the plurality of metallic tubes become the second flow passage. This makes it possible to readily construct the liquid cooling jacket. It is also possible to readily change the number of the second flow passages and a cross sectional area of the second flow passage by changing the number of the metallic tubes to be bundled and the size thereof as appropriate.

The aforementioned liquid cooling jackets may further include a metallic tube having a plurality of inner holes, wherein each of the inner holes is the second flow passage.

In accordance with the liquid cooling jackets, it is possible to readily construct the liquid cooling jackets, using the metallic tube having the plurality of inner holes.

The aforementioned liquid cooling jackets may further include a plurality of metallic fins arranged at a predetermined interval, wherein a space between the adjacent fins is the second flow passage.

In accordance with the liquid cooling jackets, because the space between the adjacent fins is the second flow passage, it is possible to transmit the heat generated by the heating element to the heat transmission fluid flowing through the second flow passage via the plurality of the fins.

In the aforementioned liquid cooling jackets, a width W of the second flow passage may be 0.2˜1.0 mm.

In accordance with the liquid cooling jackets, it is possible to make the thermal resistance and the pressure loss of the heat transmission fluid flowing inside the liquid cooling jackets to be within a preferable range.

In the aforementioned liquid cooling jackets, the width W of the second flow passage and a thickness T of the fins disposed between the adjacent second flow passages may satisfy Formula 1.

−0.375×W+0.875≦T/W≦−1.875×W+3.275  Formula 1

In accordance with the liquid cooling jackets, the thermal resistance decreases and the heat can be efficiently exchanged between the heating element and the heat transmission fluid.

In the aforementioned liquid cooling jackets, a depth D of the second flow passage and the width W of the second flow passage may satisfy Formula 2.

5×W+1≦D≦−16.25×W+2.75  Formula 2

In accordance with the liquid cooling jackets, the thermal resistance decreases and the heat can be efficiently exchanged between the heating element and the heat transmission fluid.

The aforementioned liquid cooling jackets may further comprise a fin member comprising the plurality of metallic fins and a base from which the plurality of metallic fins is extended, a jacket body for housing the fin member, wherein the base is heat-exchangeably fixed to the jacket body.

The aforementioned liquid cooling jackets can be constructed, for example, by the following process. At first, a fin member comprising the plurality of fins is manufactured by cutting a metallic extrusion having a plurality of protruded lines, which is a plurality of fins extended from a base plate, and a base which is the base plate. Then, the fin member is fixed to a box-shaped jacket body.

The aforementioned liquid cooling jackets may further comprise a first fin member comprising a first base and a plurality of first fins extended from the first base, a second fin member comprising a second base and a plurality of second fins extended from the second base, wherein the first fin member and the second fin member are combined such that the plurality of the first fins and the plurality of the second fins are interlocked together, the plurality of metallic fins are composed of the first fins and the second fins, and the second flow passage is formed between the first fin and the second fin adjacent to each other.

In accordance with the liquid cooling jackets, because the plurality of the first fins and the plurality of the second fins are interlocked together, even if an interval of each of the first fins and that of each of the second fins are wide, an interval of the adjacent fins, that is an interval of the first fin and the second fin can be made narrow.

In the aforementioned liquid cooling jackets, the heating element may be installed on the side of the first base, a protruding length of the first fin may be set to be equal to or shorter than a protruding length of the second fin, and the plurality of the second fins may be thermally connected to the first base.

In accordance with the liquid cooling jackets, because the protruding length of the first fin is set to be equal to or shorter than the protruding length of the second fin, when the first fin member and the second fin member are combined, the plurality of the second fins are ensured to be in contact with the first base. Then, the plurality of the second fins is heat-exchangeably connected to the first base to construct the liquid cooling jackets.

The heat generated by the heating element installed on the side of the first base is transmitted to both of the plurality of the first fins and the plurality of the second fins via the first base. Thus, the heat can be transmitted to the heat transmission fluid flowing through the second flow passage between the first fin and the second fin.

The aforementioned liquid cooling jackets may further comprise a jacket body comprising a fin housing for housing the plurality of the metallic fins, a sealing member for sealing the fin housing, wherein a contact area where a peripheral wall of the jacket body surrounding the fin housing and the sealing member are in contact with each other may be friction stir welded, and a start end of the area which is friction stir welded may overlap with a finish end of the area which is friction stir welded.

In accordance with the liquid cooling jackets, because the start end of the area which is friction stir welded overlaps with the finish end of the area which is friction stir welded, it is possible to securely connect the peripheral wall of the jacket body with the sealing member. This makes it difficult for the heat transmission fluid to leak.

Further, because the sealing member and the jacket body are connected by the friction stir welding without using a brazing filler metal and the like, the heat transmission fluid is not contaminated by the brazing filler metal and the like, and furthermore, devices constituting the liquid cooling system, such as a micro pump and a radiator are not corroded by the brazing filler metal and the like.

In the aforementioned liquid cooling jackets, the plurality of metallic fins may be extended from the sealing member and integrally formed with the sealing member.

In accordance with the liquid cooling jackets, because the plurality of metallic fins and the sealing member are integrally formed, the fin housing can be sealed by the sealing member, and the plurality of metallic fins can be disposed at a predetermined position in the fin housing. Therefore, manufacturing process of the liquid cooling jackets can be simplified, which makes it easy to manufacture the liquid cooling jackets, and the manufacturing cost can be also reduced. The sealing member integrally formed with the plurality of metallic fins is, for example, constructed by skiving an aluminum alloy plate as shown in a fifth embodiment of the present invention, which is described later.

If the fins and the sealing member are integrally formed by the skive process, the fins and the sealing member do not have to be connected by the brazing filler metal and the like. Therefore, the heat transmission fluid can be prevented from being contaminated by the brazing filler metal and the like.

Furthermore, because the fins and the sealing member are single-membered, the heat conductivity between the fins and the sealing member is high. Therefore, the heat of the heating element is efficiently transmitted to the plurality of fins via the sealing member when the heating element such as a CPU is installed at the sealing member. Thus, heat radiation performance of the heating element in the liquid cooling jackets becomes high.

In the aforementioned liquid cooling jackets, the peripheral wall may be friction stir welded with a jig holding the peripheral wall so that the peripheral wall does not protrude outward.

In accordance with the liquid cooling jackets, because the peripheral wall is friction stir welded with the jig holding the peripheral wall, the peripheral wall does not protrude outward easily. Even if the peripheral wall is thin, and an interval between an outer surface of a shoulder of a tool used for the friction stir welding and the outer surface of the peripheral wall is less than or equal to, for example, 2.0 mm, it is possible to carry out the friction stir welding without making the peripheral wall protrude outward when the jig holds the peripheral wall as described above.

In the aforementioned liquid cooling jackets, a length of a pin of a tool to be used in the friction stir welding may be less than or equal to 60% of a thickness of the sealing member.

In accordance with the liquid cooling jackets, by making the length of the pin of the tool to be less than or equal to 60% of the thickness of the sealing member, the sealing member becomes not to protrude toward the fin housing easily in the friction stir welding. Thus, a volume of the fin housing can be prevented from being reduced.

In the aforementioned liquid cooling jackets, a position where the tool is pulled apart may not overlap with the contact area in the friction stir welding.

In accordance with the liquid cooling jackets, because the position where the tool is pulled apart does not overlap with the contact area, a trace of the pin which is pulled apart does not remain in the contact area. Thus, the jacket body and the sealing member can be securely connected.

The aforementioned liquid cooling jackets may further comprise a metallic honeycomb member comprising a plurality of minute holes, wherein each of the plurality of minute holes is the second flow passage.

In accordance with the liquid cooling jackets, because each of the plurality of minute holes is the second flow passage, the heat of the heating element can be transmitted to the heat transmission fluid flowing through the second passage via the honeycomb member.

The aforementioned liquid cooling jackets may further comprise a ripple cross-section metallic heat dissipating sheet and a metallic jacket body to which the heat dissipating sheet is heat-exchangeably fixed, wherein the second flow passage is formed between the heat dissipating sheet and the jacket body.

The liquid cooling jackets can be easily constructed by heat-exchangeably fixing the ripple cross-section metallic heat dissipating sheet to the jacket body.

In the aforementioned liquid cooling jackets, the metal may be aluminum or aluminum alloy.

In accordance with the liquid cooling jackets, by using aluminum and aluminum alloy as the metal, a weight of the liquid cooling jackets can be reduced.

In the aforementioned liquid cooling jackets, a heat transmission fluid inlet communicating with the first flow passage and a heat transmission fluid outlet communicating with the third passage may be arranged symmetric with respect to the heating element.

In accordance with the liquid cooling jackets, the heat transmission fluid supplied to the first flow passage from the inlet is easy to flow through second flow passages which are close to the heating element. Thus, the heat can be efficiently exchanged between the heat transmission fluid and the heating element.

In the aforementioned liquid cooling jackets, the inlet and outlet may be arranged relatively away from each other.

In accordance with the liquid cooling jackets, the heat transmission fluid supplied from the inlet to the first flow passage is easy to flow through the whole of the plurality of the second flow passages. Thus, the heat can be efficiently transmitted between the heat transmission fluid flowing through the whole of the plurality of the second passage and the heating element.

In the aforementioned liquid cooling jackets, the inlet and the outlet may be arranged such that the inlet and the outlet come closer to the heating element.

In accordance with the liquid cooling jackets, the heat transmission fluid supplied to the first flow passage from the inlet is easy to flow through the second flow passages which are close to the heating element in high flow speed. Thus, the heat can be efficiently transmitted between the heat transmission fluid flowing through the second flow passages close to the heating element in high flow speed, and the heating element. For example, even if the heating element such as a CPU is not installed at the liquid cooling jackets via a heat dissipating sheet 102 (see FIG. 3), which is called a heat spreader, and thus the heat of the heating element is difficult to be transmitted to the whole of the liquid cooling jackets, the liquid cooling jackets can be radiated efficiently by making the heat transmission fluid to flow through the second flow passages close to the heating element in high flow speed.

In the aforementioned liquid cooling jackets, the heating element may be a CPU.

In accordance with the liquid cooling jackets, the heat is efficiently exchanged between the CPU and the heat transmission fluid, and thus the CPU can be cooled.

According to the present invention, there is provided a liquid cooling jacket capable of efficiently cooling a heating element such as a CPU. Other features, advantages and aspects of the present invention will be apparent from the following illustrative and non-restrictive description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a liquid cooling system according to a first embodiment.

FIG. 2 is a perspective view of a liquid cooling jacket according to the first embodiment.

FIG. 3 is a bottom perspective view of the liquid cooling jacket according to the first embodiment.

FIG. 4 is a perspective view of the liquid cooling jacket according to the first embodiment, in which a lid unit is omitted.

FIG. 5 is a plain view of the liquid cooling jacket according to the first embodiment.

FIG. 6 is a cross-sectional view of the liquid cooling jacket according to the first embodiment along a line X-X shown in FIG. 2.

FIG. 7 is an exploded perspective view of the liquid cooling jacket according to the first embodiment.

FIG. 8 is a graph schematically showing an effect of the liquid cooling jacket according to the first embodiment.

FIG. 9 is a perspective view of a liquid cooling jacket according to a second embodiment, in which a lid unit is omitted.

FIG. 10 is a cross-sectional view of the liquid cooling jacket according to the second embodiment along a line Y-Y shown in FIG. 9.

FIG. 11 is a perspective view of a liquid cooling jacket according to a third embodiment.

FIG. 12 is a plain view of the liquid cooling jacket according to the third embodiment.

FIG. 13 is a perspective view of a liquid cooling jacket according to a fourth embodiment, in which a lid unit is omitted.

FIG. 14 is a cross-sectional view of the liquid cooling jacket according to the fourth embodiment along a line Z-Z shown in FIG. 13.

FIG. 15 is an enlarged view of the cross-sectional view along the line Z-Z shown in FIG. 14.

FIG. 16 is a perspective view of a first manufacture method of a fin member of the liquid cooling jacket according to the fourth embodiment; FIG. 16A shows an extrusion before it is cut; and FIG. 16B shows the fin member after the extrusion is cut.

FIG. 17 is a perspective view of a second manufacture method of a fin member of the liquid cooling jacket according to the fourth embodiment; FIG. 17A shows an extrusion before it is cut; and FIG. 17B shows the fin member after the extrusion is cut.

FIG. 18 is a perspective view showing a friction stir welding according to the fourth embodiment.

FIG. 19 is a cross-sectional view showing the friction stir welding according to the fourth embodiment.

FIG. 20 is a plain view showing movement of a tool to be used for the friction stir welding.

FIG. 21 is a cross-sectional view of a liquid cooling jacket according to a fifth embodiment.

FIG. 22 is an enlarged view of the cross-sectional view shown in FIG. 21.

FIG. 23 is a view showing a manufacture method of a fin member of the liquid cooling jacket according to the fifth embodiment; FIG. 23A shows the fin member during a skive process; and FIG. 23B shows the fin member after the skive process has completed.

FIG. 24 is a view showing the manufacture method of the fin member of the liquid cooling jacket according to the fifth embodiment, illustrating the fin member after parts of the skive fins are removed.

FIG. 25 is a cross-sectional view showing a friction stir welding according to the fifth embodiment.

FIG. 26 is a cross-sectional view of a liquid cooling jacket according to a sixth embodiment; FIG. 26A shows the liquid cooling jacket after assembled; and FIG. 26B shows the liquid cooling jacket before assembled.

FIG. 27 is a cross-sectional view of a liquid cooling jacket according to a seventh embodiment; FIG. 27A shows the liquid cooling jacket after assembled; and FIG. 27B shows the liquid cooling jacket before assembled.

FIG. 28 is a cross-sectional view of a liquid cooling jacket according to an eighth embodiment; FIG. 28A shows the liquid cooling jacket after assembled; and FIG. 28B shows the liquid cooling jacket before assembled.

FIG. 29 is a plane view of a liquid cooling jacket according to a ninth embodiment.

FIG. 30 is a plane view of a liquid cooling jacket according to a tenth embodiment.

FIG. 31 is a graph showing a relationship between the number of times the coolant is turned and thermal resistance.

FIG. 32 is a cross-sectional view of a flat tube bundle according to a modification.

FIG. 33 is a cross-sectional view of a liquid cooling jacket according to a modification;

FIG. 33A shows the liquid cooling jacket after assembled; and FIG. 33B shows the liquid cooling jacket before assembled.

FIG. 34 is a cross-sectional view of a liquid cooling jacket according to a modification.

FIG. 35 is a perspective view of a liquid cooling jacket according to a modification.

FIG. 36 is a graph showing a relationship between a groove width W1 and heat resistance, and a relationship between the groove width W1 and a pressure loss.

FIG. 37 is a graph showing a relationship between a fin thickness T1 divided by the groove width W1 and heat resistance.

FIG. 38 is a graph showing a relationship between the groove width W1 and the fin thickness T1 divided by the groove width W1.

FIG. 39 is a graph showing a relationship between a groove depth D1 and thermal resistance.

FIG. 40 is a graph showing a relationship between the groove width W1 and the groove depth D1.

DESCRIPTION OF SYMBOLS

-   A1: First flow passage -   B1: Second flow passage group -   B1 a: Second flow passage -   C1: Third flow passage -   J1: Liquid cooling jacket -   10: Jacket body -   10 a: Space -   10 c: Space -   11: Bottom -   12: Peripheral wall -   15: Step portion -   20: Flat tube bundle -   21: Flat tube -   21 a: Inner hole -   21 b: Peripheral wall -   21 c: Partition wall -   31: Lid body -   31 a: Inlet -   31 b: Outlet -   101: CPU (Heating element) -   200: Tool -   201: Pin -   202: Shoulder -   210: Jig -   K: Friction stir welded portion -   L5: Pin length -   L6: Length between the outer surface of the tool and the outer     surface of the peripheral wall -   P1: Contact area -   Q: Overlapped area -   T1: Thickness of Fin -   T2: Thickness of Lid body -   T11: Thickness of peripheral wall -   W1: Groove width -   W11: Width of the step portion

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings

First Embodiment

A liquid cooling system and a liquid cooling jacket according to a first embodiment are now described with reference to FIG. 1 to FIG. 8. FIG. 1 is a block diagram of the liquid cooling system according to the first embodiment. FIG. 2 is a perspective view of a liquid cooling jacket according to the first embodiment. FIG. 3 is a bottom perspective view of the liquid cooling jacket according to the first embodiment. FIG. 4 is a perspective view of the liquid cooling jacket according to the first embodiment, in which a lid unit is omitted. FIG. 5 is a plain view of the liquid cooling jacket according to the first embodiment, in which an inlet pile and an outlet pipe are omitted. FIG. 6 is a cross-sectional view of the liquid cooling jacket according to the first embodiment along a line X-X shown in FIG. 2. FIG. 7 is an exploded perspective view of the liquid cooling jacket according to the first embodiment. FIG. 8 is a graph schematically showing an effect of the liquid cooling jacket according to the first embodiment.

Construction of the Liquid Cooling System

As shown in FIG. 1, a liquid cooling system S1 according to the first embodiment is a system equipped in a personal computer 120 (an electronic device) which is a tower configuration. The liquid cooling system S1 cools a CPU 101 (heating element) constituting the personal computer 120. The liquid cooling system S1 mainly comprises a liquid cooling jacket to which the CPU 101 is installed at a predetermined position, a radiator 121 (radiation means) for radiating heat transmitted by coolant (heat transmission fluid) outside, a micro pump 122 (heat transmission fluid supply means) for circulating the coolant, a reserve tank 123 for absorbing expansion and contraction of the coolant caused by changes in temperature, a flexible tube 124 for connecting these components, and the coolant for transmitting the heat. As the coolant, ethylene glycol antifreeze liquid is used for example.

Once the micro pump 122 starts to operate, the coolant circulates through the above devices.

Construction of the Liquid Cooling Jacket

The liquid cooling jacket J1 constituting the liquid cooling system S1 is now described in detail. As shown in FIG. 2 and FIG. 3, the CPU 101 is installed at a center (predetermined position) of a bottom (back side) of the liquid cooling jacket J1 via a heat dissipating sheet 102 (heat spreader). When the CPU 101 is installed as described above and the coolant flows inside of the liquid cooling jacket J1, the liquid cooling jacket J1 receives heat generated by the CPU 101 and dissipates the heat to the coolant flowing inside of the liquid cooling jacket J1. Thus, the liquid cooling jacket J1 transmits the heat received from the CPU 101 to the coolant. As a result, the CPU 101 is efficiently cooled. The heat dissipating sheet is a sheet used for efficiently transmitting the heat of the CPU 101 to a bottom 11 of a jacket body 10, which will be described later. The heat dissipating sheet is formed of metal having high thermal conductivity such as copper, for example.

As shown in FIG. 4 to FIG. 7, the liquid cooling jacket J1 (mainly) comprises the jacket body 10, a flat tube bundle 20 (tube bundle), and a lid unit 30. Unless specifically indicated, the jacket body 10, the flat tube bundle 20 and the lid unit 30 are formed of aluminum or aluminum alloy. Thus, the weight of the liquid cooling jacket J1 is reduced, and it is easy to handle the liquid cooling jacket J1.

The Jacket Body

The jacket body 10 is a shallow box of which upper side (one side) is opened (see FIG. 7). The jacket body 10 comprises a bottom 11, a peripheral wall 12, and a housing for housing the flat tube bundle 20 (see FIG. 7). The jacket body 10 is formed, for example, by die casting, metal casting, forging and the like. The jacket body 10 also comprises a fitting portion 14 of which shape corresponds to a notch 31 c of a lid body 31, which will be described later, at a part of an opening end.

The Flat Tube Bundle

The flat tube bundle 20 is heat-exchangeably bonded and fixed to the bottom 11 of the jacket body 10 by brazing filler metal formed of Al—Si—Zn alloy and the like while a space 10 a and a space 10 c are ensured to be left at both ends of the jacket body 10 (see FIG. 4 and FIG. 5). The space 10 a has a function of a first flow passage A1, and the space 10 c has a function of a third flow passage C1.

The flat tube bundle 20 is formed by bundling a predetermined number of flat tubes 21 in the thickness direction and connecting the flat tubes 21 (see FIG. 6 and FIG. 7). Each of the flat tubes 21 comprises one or a plurality of inner holes 21 a (two inner holes in the first embodiment). Each of the inner holes 21 a has a function of a second flow passage B1 a. That is, each of the second flow passages has a cross-sectional rectangular shape, and is surrounded by side wall portions (second flow passage components) formed by peripheral walls 21 b, 21 b of the flat tubes 21 that are placed at both ends of the second flow passage, an upper wall portion (a second flow passage component) formed by the peripheral wall 21 b or a partition wall 21 c, and a lower wall portion formed by the peripheral wall 21 b or the partition wall 21 c (a second flow passage component). Thus, the flat tube bundle 20 comprises a plurality of the second flow passages B1 a, which constitutes a second flow passage group B1.

The CPU 101 is installed in substantially center of the back side (out side) of the bottom 11 (see FIG. 3). Thus, the heat of the CPU 101 is transmitted to the peripheral walls 21 b surrounding the inner holes 21 a (second flow passages B1 a) of each of the flat tubes and the partition walls 21 c partitioning off the adjacent inner holes 21 a. Then, the heat transmitted to the peripheral walls 21 b and the partition walls 21 c (heat exchange portion) further transmits to the coolant flowing through each of the second flow passages. Thus, the CPU 101 mainly dissipates the heat to the coolant flowing through the second flow passage group.

Because the flat tube bundle 20 is formed by bundling a plurality of the flat tubes 21, the peripheral walls 21 b (a heat exchange portion) which directly dissipates the heat to the coolant increase. As a result, the heat can be efficiently exchanged between the CPU 101 and the coolant. Thus, the CPU 101 can be efficiently cooled.

The First Flow Passage, the Second Flow Passage Group and the Third Flow Passage

The first flow passage A1, the second flow passage group B1 (a plurality of second flow passages B1 a) and the third flow passage C1 are further described.

The first flow passage A1 is a flow passage to which the coolant is supplied from the micro pump 122. The first flow passage A1 is disposed on the side of the micro pump 122, which is upstream of the second flow passage group. The second flow passage group B1 is disposed at downstream of the first flow passage A1, and each of the second flow passages constituting the second flow passage group B1 is branched from the first flow passage A1. Thus, the coolant is distributed from the first flow passage A1 to flow into each of the second flow passages. The third flow passage C1 is disposed downstream of the second flow passage group B1, that is, downstream of the plurality of the second flow passages. The third flow passage C1 also collects the plurality of the second flow passages B1 a. Thus, the coolant flowing out of each of the second flow passages B1 a is collected by the third flow passage C1 and then discharged from the liquid cooling jacket J1.

A cross-sectional area of the first flow passage A1 and the third flow passage C1 is set to be larger than a cross-sectional area of each of the second flow passages B1 a. A length of each of the second flow passages B1 a (a length of each of the flat tubes 21) is remarkably shorter than that of only one flow passage meandering through all parts of a flat tube bundle according to the conventional art.

Thus, the coolant flowing through the first flow passage A1, the second flow passages B1 a and the third flow passage C1 in order is not subjected to almost any pressure loss. The pressure loss of the coolant in each of the second flow passages B1 a is also remarkably lower than a pressure loss that a coolant would receive in the only one meandering flow passage. Thus, a declared power of the micro pump 122 supplying the coolant to the liquid cooling jacket J1 can be reduced. Accordingly, the micro pump 122 can be small-sized and the noise thereof can be also reduced.

The Lid Unit

As shown in FIG. 7, the lid unit 30 (mainly) comprises a lid body 31, an inlet pipe 32 and an outlet pipe 32.

The Lid Body

The lid body 31 is connected and fixed to the jacket body 10 as if a lid is put on the jacket body 10 accommodating the flat tube bundle 20. An inlet 31 a which communicates with the first flow passage A1 (space 10 a) and an outlet 31 b which communicates with the third flow passage C1 (space 10 c) are formed on the lid body 31 (see FIG. 7).

The lid body 31 also comprises the notch 31 c formed by being cut out. The shape of the notch 31 c corresponds to the fitting portion 14 of the jacket body 10. Thus, the lid body 31 (lid unit 30) is combined with the jacket body 10 only in a predetermined direction.

The Inlet and the Outlet

As shown in FIG. 5, the inlet 31 a and outlet 31 b are arranged symmetric with respect to the CPU 101 in a plane view. The inlet 31 a and outlet 31 b are also arranged relatively away from each other in a plain view. In other words, the inlet 31 a, outlet 31 b and the CPU 101 are disposed on a diagonal line of the liquid cooling jacket J1, which is square in a plane view. To be more specific, the inlet 31 a is disposed on an upper left side in FIG. 5, and the outlet 31 b is disposed on a lower right side in FIG. 5 while the CPU 101 is disposed at approximately middle of the inlet 31 a and outlet 31 b (approximately center of the square liquid cooling jacket). Thus, the coolant from the inlet pipe 32 is supplied substantially evenly to the whole of the second flow passage group B1 (the whole of the plurality of second flow passages B1 a) through the inlet 31 a and the first flow passage A1. Then, the heat is exchanged between (the whole of) the coolant flowing through the whole of the second flow passage group B1 and the CPU 101.

After that, the coolant flowing from the plurality of second flow passages B1 a is collected by the third flow passage C1. Then, the coolant is discharged from the liquid cooling jacket J1 through the outlet 31 b and the outlet pipe 33.

The Inlet Pipe and the Outlet Pipe

The inlet pipe 32 is fixed at the lid body 31. Connected to the inlet pipe 32 is a flexible tube 124 communicating with the micro pump 122 (see FIG. 1) disposed upstream of the liquid cooling jacket J1. The coolant from the micro pump 122 is supplied to the first flow passage A1 via an inner hole of the inlet pipe 32 and the inlet 31 a.

The outlet pipe 33 is fixed at the lid body 31. Connected to the outlet pipe 33 is a flexible tube 124 communicating with the radiator 121 (see FIG. 1) disposed downstream of the liquid cooling jacket J1. Then, the coolant is discharged from the liquid cooling jacket J1 through the outlet 31 b and the inner hole of outlet pipe 33.

The inlet pipe 32 and outlet pipe 33 are fixed on the top surface of the lid body 31 such that the inlet pipe 32 and outlet pipe 33 stand on the top surface of the lid body 31. Therefore, the flexible tubes 124, 124 can be connected to the inlet pipe 32 and the outlet pipe 33 only from the upper surface of liquid cooling jacket J1. Thus, it is easy to pipe the flexible tubes 124, 124 (see FIG. 1) even in the personal computer 120 of which space is limited.

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J1 are now described.

The CPU 101 starts to operate and heat up when the personal computer 120 (see FIG. 1) is powered on. Then, the heat of the CPU 101 is transmitted to the bottom 11 of the jacket body 10 via the heat dissipating sheet 102. The heat is further transmitted to the peripheral walls 21 b and the partition wall 21 c of each of the flat tubes 21 constituting the flat tube bundle. When the personal computer 120 is powered on, the micro pump 122 also starts to operate, and the coolant begins circulating. The coolant flows the first flow passage A1, the second flow passage group B1 (the plurality of the second flow passages B1 a) and the third flow passage C1 in order in the liquid cooling jacket J1.

Then, the heat is exchanged between the peripheral walls 21 b and the partition wall 21 c of each of the flat tubes 21 and the coolant flowing through the plurality of the second flow passages B1 a. The heat of the CPU 101 transmitted to the peripheral walls 21 b and the partition wall 21 c is further transmitted to the coolant, and thus the coolant receives the heat.

The coolant having received the heat in each of the second flow passages B1 a is collected by the third flow passage C1 and then discharged from the liquid cooling jacket J1 via the outlet 31 b and the outlet pipe 33.

The discharged coolant is supplied to the radiator 121 through the flexible tube 124. The heat of the coolant is dissipated in the radiator 121. The coolant of which temperature is lowered flows into the micro pump 122 through the reserve tank 123 and flexible tube 124, and then supplied to the liquid cooling jacket J1 again.

By repeating the processes of

-   (1) Transmission of the heat to the heat dissipating sheet 102, the     bottom 11, the peripheral walls 21 b and the partition wall 21 c of     each of the flat tubes 21, -   (2) Transmission of the heat to the coolant from the peripheral     walls 21 b and the partition wall 21 c, and -   (3) Dissipation of the heat of the coolant in the radiator 121,     the CPU 101 is efficiently cooled.

The heat of the CPU 101 is distributed to the peripheral walls 21 b and the partition wall 21 c of the plurality of the flat tubes 21. The heat of the peripheral walls 21 b and the partition wall 21 c is further transmitted to the coolant flowing through each of the plurality of the second flow passages B1 a. Thus, the CPU 101 can be efficiently cooled.

Moreover, the coolant supplied to the liquid cooling jacket J1 flows into the plurality of the second flow passages B1 a (the second flow passage group B1) which exchanges the heat, and has the shorter passage length via the first flow passage A1 of which cross sectional area is large. Then, the coolant is collected by the third flow passage C1 having a large cross sectional area. Therefore, the pressure loss the coolant is subjected to in the liquid cooling jacket J1 becomes small. As a result, the micro pump 122 can be small sized and an applicable range of the liquid cooling jacket J1 becomes wide.

Furthermore, in accordance with the liquid cooling jacket J1 (the present invention), the coolant can flow in smaller pressure loss and higher flow rate, compared with the liquid cooling jacket according to the conventional art, which comprises the only one long meandering second flow passage as shown in FIG. 8. As shown in FIG. 8, an intersection M2 of a pressure loss—flow rate curve according to the present invention and a pressure loss—flow rate curve of a micro pump is shifted right-ward compared to a intersection M1 of a pressure loss—flow rate curve according to the conventional art and the pressure loss—flow rate curve of the micro pump. This indicates the pressure loss becomes small and the flow rate becomes high in accordance with the present invention.

Manufacture Method of the Liquid Cooling Jacket

A manufacture method of the liquid cooling jacket J1 is now described with reference to FIG. 7. The manufacture method of the liquid cooling jacket J1 mainly comprises steps of: a first step of manufacturing the flat tube bundle 20, and a second step of bonding and fixing the flat tube bundle 20 to the jacket body 10.

First Step

The plurality of the flat tubes 21 is connected and bundled by an appropriate means. Then, both ends of the flat tubes bundled are cut and grinded to manufacture the flat tube bundle 20.

Second Step

The flat tube bundle 20 is heat-exchangeably bonded and fixed to the predetermined position of the bottom 11 of the jacket body 10 by an appropriate means (fluxed with Al—Si—Zn brazing filler material). The space 10 a (first flow passage A1) and the space 10 c (third flow passage C1) are ensured to be left at both ends of the flat tube bundle 20 when the flat tube bundle 20 is fixed to the jacket body 10.

After that, the lid body 31 to which the inlet pipe 32 and outlet pipe 33 are fixed at a predetermined position is connected and fixed to the jacket body 10. Thus, the liquid cooling jacket J1 is obtained.

It is to be noted that the inlet pipe 32 and outlet pipe 33 may be fixed to the lid body 31 after the lid body 31 is fixed to the jacket body 10.

As described above, in accordance with the manufacture method of the liquid cooling jacket J1 according to the first embodiment, the liquid cooling jacket J1 can be obtained by a simple process of making the flat tube bundle 20 from the plurality of the flat tubes 21, fixing the flat tube bundle 20 to the jacket body 10, and fixing the lid body 31 to the jacket body 10.

Second Embodiment

A liquid cooling jacket according to a second embodiment is now described with reference to FIG. 9 and FIG. 10. FIG. 9 is a perspective view of a liquid cooling jacket J2 according to the second embodiment, in which a lid unit is omitted.

FIG. 10 is a cross-sectional view of the liquid cooling jacket J2 according to the second embodiment along a line Y-Y shown in FIG. 9.

As shown in FIG. 9 and FIG. 10, the liquid cooling jacket J2 according to the second embodiment comprises a flat tube bundle 23 instead of the flat tube bundle 20 of the liquid cooling jacket J1 according to the first embodiment. Although the flat tube bundle 23 is the same as the flat tube bundle 20 in outside dimension, the flat tube bundle 23 is formed by bundling a plurality of laminar flat tubes 24 (three laminar flat tubes in FIG. 9 and FIG. 10). Each of the flat tubes 24 comprises a plurality of inner holes (12 inner holes in FIG. 9 and FIG. 10) inside thereof. Each of the inner holes is a second flow passage B2 a. As a result, the flat tube bundle 23 comprises a second flow passage group B2 including a plurality of the second flow passages B2 a.

Because each of the flat tubes 24 is laminar, the number of the inner holes 24 a bored in the flat tube 24 (12 inner holes in FIG. 9) is larger than the number of the inner holes 21 a bored in the flat tube 21 (2 inner holes) according to the first embodiment. Therefore, the number of the flat tubes 24 (3 flat tubes) constituting the flat tube bundle 23 is less than the number of the flat tubes 21 (20 flat tubes in FIG. 7) constituting the flat tube bundle 20 according to the first embodiment. Thus, in accordance with the flat tube bundle 23 according to the second embodiment, the number of the flat tubes 24 to be bundled can be reduced compared to that of the flat tube bundle 20 according to the first embodiment. Thus, the flat tube bundle 23 can be easily manufactured without much labor.

Third Embodiment

A liquid cooling jacket according to a third embodiment is now described with reference to FIG. 11 and FIG. 12. FIG. 11 is a perspective view of the liquid cooling jacket according to the third embodiment. FIG. 12 is a plain view of the liquid cooling jacket according to the third embodiment.

Configuration of the Liquid Cooling Jacket

As shown in FIG. 11 and FIG. 12, the liquid cooling jacket J3 according to the third embodiment comprises a lid body 34 on which an inlet 34 a and an outlet 34 b are disposed in positions different from those of the liquid cooling jacket J1 according to the first embodiment.

The inlet 34 a communicates with substantially center of the space 10 a (first flow passage A1). The coolant is supplied to the substantially center of the space 10 a. The outlet 34 b communicates with substantially center of the space 10 c (third flow passage C1). The coolant is discharged from the substantially center of the space 10 c. The inlet 34 a and outlet 34 b are disposed symmetric with respect to the CPU 101 in a plain view. The inlet 34 a and the outlet 34 b are also arranged such that the inlet 34 a and the outlet 34 b come closer to the heating element in the plain view.

Similar to the lid body 31 according to the first embodiment, the lid body 34 comprises a notch 34 c of which shape corresponds to the fitting portion 14 of the jacket body 10.

Effects of the Jacket Body

Effects of the liquid cooling jacket J3 are now briefly described.

The coolant supplied to the first flow passage A1 from the inlet 34 a is easy to flow through second flow passages which are close to the CPU 101. Thus, the heat can be efficiently exchanged between the coolant and the CPU 101, and thus the CPU 101 can be efficiently cooled.

Fourth Embodiment

A liquid cooling jacket according to a fourth embodiment is now described with reference to FIG. 13 to FIG. 20. FIG. 13 is a perspective view of the liquid cooling jacket according to the fourth embodiment, in which a lid unit is omitted. FIG. 14 is a cross-sectional view of the liquid cooling jacket according to the fourth embodiment along a line Z-Z shown in FIG. 13. FIG. 15 is an enlarged view of the cross-sectional view along the line Z-Z shown in FIG. 14. FIG. 16 is a perspective view of a first manufacture method of a fin member of the liquid cooling jacket according to the fourth embodiment; FIG. 16A shows an extrusion before it is cut; and FIG. 16B shows the fin member after the extrusion is cut. FIG. 17 is a perspective view of a second manufacture method of a fin member of the liquid cooling jacket according to the fourth embodiment; FIG. 17A shows an extrusion before it is cut; and FIG. 17B shows the fin member after the extrusion is cut. FIG. 18 is a perspective view showing a friction stir welding according to the fourth embodiment. FIG. 19 is a cross-sectional view showing the friction stir welding according to the fourth embodiment. FIG. 20 is a plain view showing movement of a tool to be used for the friction stir welding.

Construction of the Liquid Cooling Jacket

As shown in FIG. 13 and FIG. 14, the liquid cooling jacket according to the fourth embodiment comprises a fin member 25 formed of aluminum or aluminum alloy instead of the flat tubes 20 according to the first embodiment.

The liquid cooling jacket according to the fourth embodiment also comprises a fin housing for housing the fin member 25. The fin housing is surrounded by the peripheral wall 12. The fin member 25 is fixed to the bottom 11 by brazing and housed in the fin housing. The fin housing is sealed by putting the lid body 31 on an opening of the jacket body 10 (see FIG. 14).

The Fin Member

As shown in FIG. 14, the fin member 25 comprises a base 25 a and a plurality of fins 25 b extended from the base 25 a. The base 25 a is heat-exchangeably bonded and fixed to the bottom 11 of the jacket body 10. Thus, the heat of the CPU 101 is transmitted to each of the fins 25 b via the heat dissipating sheet 102 and the bottom 11. A top end of each of the fins 25 b is in contact with a back side of the lid body 31. Preferably, the base 25 a and the jacket body 10 are securely heat-exchangeably bonded by the brazing filler material formed of Al—Si—Zn alloy.

An interval between the adjacent fins 25 b, 25 b is a second flow passage B3 a. That is, the fin member 25 comprises a second flow passage group B3 comprising a plurality of the second flow passages B3 a. As shown in FIG. 15, the interval between the adjacent fins 25 b, 25 b, or a groove width W1, which is a width of the second flow passage B3 a is designed to be 0.2 to 1.1 mm. In accordance with this construction, thermal resistance of the liquid cooling jacket and a pressure loss the coolant flowing inside thereof is subjected to can be made to be within a preferable range as shown in another embodiment, which is described later.

The groove width W1 and a thickness T1 of the fins 25 b, or the thickness T1 of the fins 25 b disposed between the adjacent second flow passages satisfy Formula 1 below.

−0.375×W+0.875≦T1/W1≦−1.875×W+3.275  Formula 1

Thus, the thermal resistance of the liquid cooling jacket J4 becomes small, and the heat can be efficiently exchanged between the CPU 101 and the coolant.

In addition, the groove width W1 and a depth D1 (a depth of the second flow passage B3 a) satisfy Formula 2 below.

5×W+1≦D1≦−16.25×W+2.75  Formula 2

Thus, the thermal resistance of the liquid cooling jacket J4 becomes optimum.

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J4 are now briefly described.

The coolant flows through the first flow passage A1, the second flow passage group B3 (the plurality of second flow passages B3 a) and the third flow passage C1 in order. The heat is exchanged between the coolant flowing through the second flow passage group B3 and the plurality of fins 25 b. Thus, the CPU 101 can be efficiently cooled.

Manufacture Methods of the Fin Member of the Liquid Cooling Jacket

Manufacture methods of the fin member 25 of the liquid cooling jacket J4 are illustrated below.

First Manufacture Method of the Fin Member

A first manufacture method of the fin member 25 is described with reference to FIG. 16. As shown in FIG. 16A, a metallic extrusion 41 comprising a bottom plate 42, and a plurality of protruded lines 43 extended from the bottom plate 42 is manufactured by using a predetermined mold. Then, by cutting the extrusion 41 in predetermined cutting surfaces, the fin member 25 comprising the base 25 a (a part of the bottom plate 42), and a plurality of fins 25 b (a part of the plurality of the protruded lines 43) can be manufactured.

Second Manufacture Method of the Fin Member

A second manufacture method of the fin member 25 is described with reference to FIG. 17. As shown in FIG. 17A, a plurality of grooves 44 a is formed on a metallic block of which shape corresponds to the dimension of the fin member 25 by using an appropriate cutting tool. Thus, the fin member 25 comprising the base 25 a, and the plurality of fins 25 b can be manufactured (see FIG. 17B).

Assembling of the Liquid Cooling Jacket

A friction stir welding of the jacket body 10 to which the fin member 25 is attached and the lid unit 30 is described below with reference to FIG. 18 to FIG. 20.

As shown in FIG. 18, the lid unit 30 is put on the jacket body 10 to which the fin member 25 is brazed with the notch 31 c fit to the fitting portion 14. As shown in FIG. 19, an opening end of the jacket body 10 is uneven, and the lid body 31 is put on a step portion 15 which is lowered by one step. A width W11 of the step portion 15 is preferably set to be as narrow as possible so that a volume of the first flow passage A1 and the third flow passage C1 through which the coolant flows is ensured to be left. To be more specific, the width W11 is preferably set to be 0.1 to 0.5 mm.

A contact area P1 of the peripheral wall 12 and the lid body 31 is friction stir welded by using a tool 200 for the friction stir welding. When the contact area P1 is friction stir welded, a friction stir welded portion K (see FIG. 15) is formed in a rearward of the tool 200, and the peripheral wall 12 and the lid body 31 are connected. A length L5 of a pin 201 of the tool 200 is preferably set to be less than or equal to 60% of a thickness T2 of the lid body 31, which is a member to be connected. By making the length L5 of the pin 201 of the tool 200 to be less than or equal to 60% of the thickness T2, it is difficult for the contact area P1 to be protruded into inside of the jacket body 10 by a pressing force of the tool 200, even if the width W11 of the step portion 15 is small, though it depends on a quality of material.

The tool 200 is controlled by a machine (not shown) such that the tool 200 rotates and moves along the contact area P1 (see FIG. 18).

When the contact area P1 is friction stir welded, an outer surface of the peripheral wall 12 of the jacket body 10 is held by an appropriate jig 210. This makes it difficult for the peripheral wall 12 to be protruded outward by the pressing force of the tool 200 even if the peripheral wall 12 is thin and a length L6 between the outer surface of the peripheral wall 12 and an outer surface of the tool 200 is less than or equal to 2.0 mm for example.

In addition to this, a top surface of the jig 210 is preferably lowered from a surface of the contact area P1 by approximately 1.0 to 2.0 mm to keep the tool 200 from contact with the jig 210 when the peripheral wall 12 is thin.

As shown in FIG. 20, the tool 200 is moved so that a start end of the area which is friction stir welded overlaps with a finish end of the area which is friction stir welded (see reference symbol Q). Thus, the peripheral wall of the jacket body 10 is securely connected with the lid body 31. This makes it difficult for the coolant to leak. Then, the pin 201 is pulled apart after the tool 200 is removed from the contact area P1. Thus, a trace which would be made when pulling the pin 201 apart is not formed on the contact area P1.

Fifth Embodiment

A liquid cooling jacket according to a fifth embodiment is now described with reference to FIG. 21 to FIG. 25. FIG. 21 is a cross-sectional view of the liquid cooling jacket according to the fifth embodiment. FIG. 22 is an enlarged view of the cross-sectional view shown in FIG. 21. FIG. 23 is a perspective view of a manufacture method of a fin member of the liquid cooling jacket according to the fifth embodiment; FIG. 23A shows the fin member during a skive process; and FIG. 23B shows the fin member after the skive process has completed. FIG. 24 is a view showing the manufacture method of the fin member of the liquid cooling jacket according to the fifth embodiment, illustrating the fin member after parts of the skive fins shown in FIG. 23 are removed. FIG. 25 is a cross-sectional view showing a friction stir welding according to the fifth embodiment.

Different features of the liquid cooling jacket according to the fifth embodiment compared with the liquid cooling jacket J4 according to the fourth embodiment are described below.

Construction of the Liquid Cooling Jacket

As shown in FIG. 21, a liquid cooling jacket J5 according to the fifth embodiment comprises a jacket body 10C and a fin member 29 formed of aluminum or aluminum alloy, wherein the CPU 101 is installed on a bottom 29 a (sealing member) of the fin member 29.

The jacket body 10C is a laminar box which opens to downside of FIG. 21 and comprises a fin housing inside of the laminar box.

As described later, the fin member 29 is formed by skiving a plate 61 (see FIG. 23A). The fin member 29 comprises the bottom 29 a and a plurality of metallic fins 29 b. The plurality of fins 29 are extended from the bottom 29 a and integrally formed with the bottom 29 a. Thus, the heat is efficiently transmitted between the bottom 29 a and the fins 29 b.

The bottom 29 a has a function of a sealing member for sealing the fin housing. Furthermore, an interval between the adjacent fins 29 b, 29 b has a function of a second flow passage B4 a (see FIG. 22). The liquid cooling jacket J5 comprises a second flow passage group B4 constituted by a plurality of the second flow passages B4 a. Similar to the fourth embodiment, when the fin member 29 is extended from the jacket body 10C, the first flow passage A1 and the third flow passage C1 are formed in the liquid cooling jacket J5 (see FIG. 13).

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J5 are now briefly described.

The coolant flows through the first flow passage A1, the second flow passage group B4 (the plurality of second flow passages B4 a) and the third flow passage C1 in order. The heat is mainly exchanged between the coolant flowing through the second flow passage group B4 and the plurality of fins 29 b. Thus, the CPU 101 can be efficiently cooled. Because the bottom 29 a and the fins 29 b are integrally formed, the heat of the CPU 101 is efficiently transmitted to the plurality of the fins 29 b. This makes it possible to radiate the heat efficiently.

Manufacture Method of the Fin Member of the Liquid Cooling Jacket

A manufacture method of the fin member 29 of the liquid cooling jacket J5 using skive process is described with reference to FIG. 23 and FIG. 24. As shown in FIG. 23A, a plate-like plate 61 is skived as described in Japanese Laid-open Patent Application No. 2001-326308 and Japanese Laid-open Patent Application No. 2001-352020. To be more specific, the plate 61 is cut by a cutting tool 62 in an acute angle to open up parts of the plate 61. Thus, a plurality of skive fins 63 is formed. By repeating the above process, a skive fin intermediate 64 comprising the plurality of skive fins 63 is manufactured (see FIG. 23B). Parts of the plate 61 which are not opened up are the bottom 29 a of the fin member 29.

Then, outer sides of the plurality of skive fins 63 are cut by a cutting tool so that the first flow passage A1 and the third flow passage C1 are formed in the liquid cooling jacket J5 when the fin member 29 and the jacket body 10 c are combined to form the liquid cooling jacket J5. Thus, the fin member 29 comprising the bottom 29 a and the plurality of fins 29 b integrally formed on the bottom 29 is obtained.

Manufacture methods of the fin member 29 are not limited to the above method. The fin member 29 may be obtained by removing parts of the fins 25 b of the fin member 25 formed by cutting the extrusion 41 according to the fourth embodiment (see FIG. 16), or by removing parts of the fins 25 b of the fin member 25 formed by grooving (see FIG. 17).

Assembling of the Liquid Cooling Jacket

As shown in FIG. 25, similar to the fourth embodiment, the jacket body 10 c and the fin member 29 is combined and a contact area P2 is friction stir welded with the jig 210 holding the jacket body 10C. The length L5 of the pin 201 of the tool 200 is less than or equal to 60% of a thickness T3 of the bottom 29 a (sealing member) of the fin member 29 which is a member to be connected.

Sixth Embodiment

A liquid cooling jacket according to a sixth embodiment is now described with reference to FIG. 26. FIG. 26 is a cross-sectional view of the liquid cooling jacket according to the sixth embodiment; FIG. 26A shows the liquid cooling jacket after assembled; and FIG. 26B shows the liquid cooling jacket before assembled.

Construction of the Liquid Cooling Jacket

As shown in FIG. 26A, the liquid cooling jacket J6 according to the sixth embodiment comprises a jacket body 10A (first fin member) and a lid unit 35 (second fin member) compared with the liquid cooling jacket J1 according to the first embodiment. The jacket body 10A comprises a bottom 11 (first base) and a plurality of fins 13 extended from the bottom 11 at a predetermined interval. The lid unit 35 comprises a lid body 36 (second base) and a plurality of fins 37 extended from the lid body 36 at a predetermined interval.

The jacket body 10A and the lid unit 35 are combined such that the plurality of fins 13 and the plurality of fins 37 interlock together. The lid unit 35 is connected and fixed to the jacket body 10A. The whole of fins of the liquid cooling jacket J6 is constituted by the plurality of fins 13 and 37 interlocked together. An interval between the adjacent fins 13 and 37 is a second flow passage B5 a, and the liquid cooling jacket J6 comprises a second flow passage group B5 comprising a plurality of second flow passages B5 a.

Thus, because the whole of fins is formed by interlocking the plurality of fins 13 and 37 together, an interval d1 between the adjacent fins 13 and an interval d2 between the adjacent fins 37 can be made wide, which makes the groove process using the cutting tool and the like easier.

A protruding length L1 of the plurality of fins 13 from the bottom 11 is set to be equal to or shorter than a protruding length L2 of the plurality of fins 37 from the lid body 36 as shown in FIG. 26B. The plurality of fins 37 are heat-exchangeably bonded and fixed to the bottom 11 by an appropriate means, and also thermally connected to the bottom 11. Thus, the heat of the CPU 101 on a side of the jacket body 10A (first base) is transmitted not only to the plurality of fins 13, but also to the plurality of fins 37.

That is, because the protruding length L1 of the plurality of fins 13 is set to be equal to or shorter than the protruding length L2 of the plurality of fins 37, top ends of the plurality of fins 37 are ensured to come into contact with the bottom 11 of the jacket 10A. Thus, the plurality of fins 37 and the bottom 11 are ensured to be thermally connected.

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J6 are now briefly described.

In accordance with the liquid cooling jacket J6, when the coolant flows through the second flow passage group B5, the heat transmitted to the plurality of fins 13 and the plurality of fins 37 is further transmitted to the flowing coolant. Thus, the CPU 101 can be efficiently cooled.

Seventh Embodiment

A liquid cooling jacket according to a seventh embodiment is now described with reference to FIG. 27. FIG. 27 is a cross-sectional view of the liquid cooling jacket according to the seventh embodiment; FIG. 27A shows the complete liquid cooling jacket after assembled; and FIG. 27B shows the liquid cooling jacket before assembled.

Construction of the Liquid Cooling Jacket

As shown in FIG. 27A and FIG. 27B, the liquid cooling jacket J7 according to the seventh embodiment comprises a metallic honeycomb member 26 comprising a plurality of minute holes 26 a instead of the flat tube bundle 20 of the liquid cooling jacket J1 according to the first embodiment.

The Honeycomb Member

The honeycomb member 26 is heat-exchangeably bonded and fixed to the bottom 11 of the jacket body 10 by an appropriate means. Therefore, the heat of the CPU 101 is transmitted to peripheral wall 26 b surrounding the minute holes 26 a. Each of the minute holes has a function of a second flow passage B6 a, through which the coolant flows. That is, the honeycomb member 26 comprises a second flow passage group B6 comprising a plurality of the second flow passages B6 a. Although the honeycomb member 26 comprises the plurality of minute holes 26 a, each of which is rectangular in cross sectional view is illustrated in FIG. 27, a shape of the minute holes 26 a is not limited to this and may be other shapes such as hexagon. Preferably, the honeycomb member 26 and the bottom 11 of the jacket 10 are securely heat exchangeably bonded together by the brazing filler metal.

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J7 are now briefly described.

The coolant flows through the first flow passage A1, the second flow passage group B6 (the plurality of second flow passages B6 a) and the third flow passage C1 in order. The heat is mainly exchanged between the peripheral wall 26 b of the honeycomb member 26 and the coolant flowing through the second flow passage group B6. The heat of the peripheral wall 26 b is transmitted to the coolant as described above. Thus, the CPU 101 can be efficiently cooled.

Eighth Embodiment

A liquid cooling jacket according to an eighth embodiment is now described with reference to FIG. 28. FIG. 28 is a cross-sectional view of the liquid cooling jacket according to the eighth embodiment; FIG. 28A shows the complete liquid cooling jacket after assembled; and FIG. 28B shows the liquid cooling jacket before assembled.

Construction of the Liquid Cooling Jacket

As shown in FIG. 28A and FIG. 28B, the liquid cooling jacket J8 according to the eighth embodiment comprises a ripple cross-section metallic heat dissipating sheet 27 (brazing sheet) instead of the flat tube bundle 20 of the liquid cooling jacket J1 according to the first embodiment.

The Heat Dissipating Sheet

The heat dissipating sheet 27 comprises a sheet body 27 a formed of Al—Mn alloy and Al—Fn—Mn alloy and the like, a brazing filler metal layer 27 b formed of Al—Si—Zn alloy on the lower side surface of the sheet body 27 a. A part of the brazing filler metal layer 27 b is molten and then cured so that the heat dissipating sheet 27 is heat-exchangeably bonded and fixed to the bottom 11 of the jacket body 10. Thus, the heat of the CPU 101 is transmitted to the heat dissipating sheet 27 via the bottom 11.

A plurality of second flow passages B7 a is formed between the heat dissipating sheet 27 and the jacket body 10 and also between the heat dissipating sheet 27 and the lid body 31. That is, the liquid cooling jacket J8 comprises a second flow passage group B7 comprising a plurality of the second flow passages B7 a.

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J8 are now briefly described.

The coolant flows through the first flow passage A1, the second flow passage group B7 (the plurality of second flow passages B7 a) and the third flow passage C1 in order. The heat is mainly exchanged between the heat dissipating sheet 27 and the coolant flowing through the second flow passages B7 a. Thus, the heat of the heat dissipating sheet 27 is transmitted to the coolant. As a result, the heat of the CPU 101 is efficiently cooled.

Ninth Embodiment

A liquid cooling jacket according to a ninth embodiment is now described with reference to FIG. 29. FIG. 29 is a plane view of the liquid cooling jacket according to the ninth embodiment. FIG. 29 illustrates the liquid cooling jacket without a lid body for an explanatory purpose.

Construction of the Liquid Cooling Jacket

As shown in FIG. 29, although the liquid cooling jacket J1 according to the first embodiment comprises the flat tube bundle 20, the liquid cooling jacket J9 according to the ninth embodiment comprises three flat tube bundles 20. The three flat tube bundles 20 are disposed in line such that the inner holes 21 a (second flow passage B1 a) of each flat tube bundle 20 face in the same direction in a jacket body 10B. The three flat tube bundles 20 are also heat-exchangeably bonded and fixed to the bottom 11 of the jacket body 10B while a space 10 d between the upstream flat tube bundle 20 and the midstream flat tube bundle 20 and a space 10 d between the midstream flat tube bundle 20 and the downstream flat tube bundle 20 are provided in the jacket body 10B.

The spaces 10 d, 10 d have a function of a fourth flow passage E1, E1 (communication flow passage) connecting the second flow passage groups B1, which are the flat tube bundles, in-line. A cross-sectional area of the fourth flow passage E1 is set to be larger than the cross-sectional area of the second flow passage B1 a constituting each second flow passage group. The liquid cooling jacket J9 according to the ninth embodiment comprises three second flow passage groups B1, B1, B1 (second flow passage group portion) disposed in line.

Effects of the Liquid Cooling Jacket

Effects of the liquid cooling jacket J9 are now briefly described.

The coolant flows through the first flow passage A1, the upstream second flow passage group B1, the fourth flow passage E1, the midstream second flow passage group B1, the fourth flow passage E1, and the third flow passage C1 in order. That is, the coolant flows through three second flow passage groups B1, B1, B1 in line. At that time, the pressure loss the coolant is subjected to in the fourth flow passage E1 becomes small because the coolant flows through the fourth flow passage E1 between the adjacent second flow passage groups B1, B1. In other words, a load applied to the micro pump 122 can be made smaller by disposing the fourth flow passage E1 which has the large cross sectional area between the second flow passage groups B1, B1, compared to the long second flow passage group without the fourth flow passages E1.

Tenth Embodiment

A liquid cooling jacket according to a tenth embodiment is now described with reference to FIG. 30 and FIG. 31. FIG. 30 is a plane view of the liquid cooling jacket according to the tenth embodiment. FIG. 31 is a graph showing a relationship between the number of second flow passage groups and the thermal resistance.

As shown in FIG. 30, similar to the liquid cooling jacket J9 according to the ninth embodiment, the liquid cooling jacket J10 according to the tenth embodiment comprises the three second flow passage groups B1, B1, B1 (second flow passage group portion) connected in series, wherein the adjacent second flow passage groups B1, B1 are connected in series in a coolant flowing direction via the fourth flow passage E1 (communication flow passage).

In the liquid cooling jacket J10, however, the adjacent second flow passages B1, B1 are disposed side by side such that a downstream end of the upper second flow passage B1 of the adjacent second flow passages B1, B1 and an upstream end of the lower second flow passage B1 of the adjacent second flow passages B1, B1 are disposed on the same side. The downstream end and the upstream end are connected in series via the fourth flow passage E1. To be more specific, the upstream second flow passage B1 and the midstream second flow passage B1 are disposed side by side in the coolant flowing direction and also in the lateral direction of FIG. 30. For example, a downstream end of the upstream second flow passage B1 and an upstream end of the midstream second flow passage B1 face toward the same side, which is a downside in FIG. 30.

In this specification, the state where the adjacent second flow passages B1, B1 are disposed side by side as described above is represented as “coolant is turned” in contrast to the ninth embodiment.

In accordance with the liquid cooling jacket J10, the coolant meanders in the liquid cooling jacket J10. This makes the thermal resistance of the liquid cooling jacket J10 to be smaller than that of the liquid cooling jacket J9 according to the ninth embodiment.

More specifically, when the size of the liquid cooling jacket in a plain view is constant, if the number of the second flow passages is increased by increasing the number of times the coolant is turned without changing the number of the second flow passages constituting each of the second passage groups, a cross-sectional area of each of the second flow passages constituting each of the second flow passage groups becomes smaller. Therefore, when the flow rate of the coolant flowing through the liquid cooling jacket is constant, if the number of the second flow passage groups is increased, a flow speed of the coolant in each of the second flow passages is increased. Thus, the heat is efficiently transmitted from the liquid cooling jacket to the coolant, and the thermal resistance of the liquid cooling jacket decreases accordingly.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and the various embodiments may be combined as appropriate as long as it does not deviate from the spirit of the present invention. For example, the embodiments of the present invention may be modified as described below.

The description has been made on the case where the heating element is the CPU 101 in each of the above embodiments; however, types of the heating element are not limited to a CPU and may be a power module, LED lamp, and the like for example.

The description has been made on the case where the flat tube bundle 20 is formed by the plurality of flat tubes 21 bundled in a thickness direction in the first embodiment, however, the flat tubes 21 may be further bundled in a width direction.

The description has been made on the case where the liquid cooling jacket J1 according to the first embodiment comprises the flat tube bundle 20 formed by the plurality of the flat tubes 21 bundled (see FIG. 6). As shown in FIG. 32, however, the liquid cooling jacket may be a liquid cooling jacket J11 comprising a flat tube 28 having a plurality of inner holes 28 a partitioned by a plurality of partition walls, instead of the flat tube bundle 20. In this case, each of the plurality of inner holes 28 a has a function of a second flow passage B8 a, and the flat tube 28 comprises a second flow passage group B8 comprising a plurality of the second flow passages B8 a.

The description has been made on the case where the inlet 31 a and the outlet 31 b are installed on the lid body 31 in the liquid cooling jacket J1 according to the first embodiment. However, positions of the inlet 31 a and the outlet 31 b are not limited to this, and the inlet 31 a and the outlet 31 b may be installed on the peripheral wall 12 of the jacket body 10 for example. Furthermore, positions of the inlet pipe 32 and the outlet pipe 33 are also not limited to the upper surface of the liquid cooling jacket J1, and may be on the side surface of the liquid cooling jacket J1.

The description has been made on the case where the fins 13 are extended from the jacket body 10A and the fins 37 are extended from the lid body 37 in the liquid cooling jacket J6 according to the sixth embodiment (see FIG. 26). As shown in FIG. 33A and FIG. 33B, however, the liquid cooling jacket may be a liquid cooling jacket J12 comprising a first fin member 50 comprising a first base 51 and a plurality of first fins 52 extended from the first base 51, and a second fin member 55 comprising a second base 56 and a plurality of second fins 57 extended from the second base 56.

The liquid cooling jacket J12 shown in FIG. 33 is further described below. The first fin member 50 and the second fin member 55 are combined such that the plurality of the first fins 52 and the plurality of the second fins 57 are interlocked together. The whole of the plurality of the metallic fins in the liquid cooling jacket J12 is constituted by the plurality of the first fins 52 and the plurality of the second fins 57. The second flow passage B9 a is formed between the first fin 52 and the second fin 57 adjacent to each other. The first fin member 50 is disposed on a side of the CPU 101 and the first base 51 is heat-exchangeably fixed to the bottom 11 of the jacket body 10.

The liquid cooling jacket J12 comprises a second flow passage group B9 comprising a plurality of the second flow passages B9 a. A protruding length L3 of the plurality of the first fins 52 from the first base 51 is set to be equal to or shorter than a protruding length L4 of the plurality of the second fins 57 from the second base 56. The plurality of the second fins 57 and the first base 51 are heat exchangeably-bonded and fixed by an appropriate means, and thus thermally connected to each other.

The first flow passage A1 and the third flow passage C1 are formed by the space 10 a and the space 10 c provided between the jacket body 10 and the flat tube bundle 20 in the first embodiment (see FIG. 5). However, a branched tube, of which inner holes are first flow passages, may be disposed outside and upstream of the jacket body 10, and a collecting tube, of which inner holes are third flow passages, may be disposed downstream.

The fin member 25 is fixed to the jacket body 10 in the liquid cooling jacket J4 according to the fourth embodiment (see FIG. 14). As shown in FIG. 34, however, the liquid cooling jacket may be a liquid cooling jacket J13 wherein the fin member 25 is fixed to a side of the lid body 31 which faces to the jacket body 10. As shown in FIG. 34, the CPU 101 may be installed on the lid body 31. Furthermore, the inlet pipe 32 which is used as a coolant inlet of the liquid cooling jacket J13 and the outlet pipe 33 which is used as a coolant outlet may be installed on the jacket body 10. In addition to this, the fins may be integrally formed with the side of the lid body 31 which faces to the jacket body 10.

Further, as shown in FIG. 35, when the jacket body 10 comprises four legs 16, each of which comprises an insertion hole 16 a through which a screw 125 is inserted, and the liquid cooling jacket J13 is installed in a casing 126 of the personal computer 120 (see FIG. 1), a position where the tool 200 is pulled apart is preferably a portion corresponding to the insertion hole 16 a. After the tool 200 is pulled apart from the part described above, the insertion hole 16 a is bored in the portion where the tool 200 is pulled apart. Thus, a trace of the pin which is pulled apart does not remain.

FIG. 34 is a cross-sectional view along a line X1-X1 in FIG. 35.

EXAMPLES

The present invention is described more specifically based on examples below.

Example 1

Analysis of the Groove Width W1 of the Second Flow Passage B3 a

In the liquid cooling jacket J4 according to the fourth embodiment (see FIG. 13), aluminum alloy members wherein the groove width W1 (see FIG. 15) of the second flow passage B3 a is 0.2 mm, 0.5 mm and 1.0 mm are manufactured. Specification of the liquid cooling jacket J4 is shown in Table 1.

An overall flow passage width W0 represents the width of the first flow passage A1 and the third flow passage C1 in Table 1. An overall length L0 represents a sum of the length of the first flow passage A1, the length of the second flow passage B3 a and the length of the third flow passage C1 in Table 1 (see FIG. 13 and FIG. 14).

TABLE 1 Heat conductivity of aluminum alloy (W/mk) 200 Overall flow passage width (mm) 100 Overall flow passage length (mm) 100 Groove width of the second flow passage B3a (mm) 0.2, 0.5, 1.0 Depth of the second flow passage B3a (mm)  10

Water is used as the coolant. A relationship between the groove width W1 and the thermal resistance of the liquid cooling jacket J4, and a relationship between the groove width W1 and the pressure loss of the liquid cooling jacket J4 are analyzed when the micro pump 122 (see FIG. 1) is operated (see FIG. 2) such that the water flows at 5 (L/min). The thermal resistance and the pressure loss are measured by an appropriate means. In the liquid cooling jacket J4 of this specification, a target thermal resistance is less than or equal to 0.008 (degree/W).

TABLE 2 Coolant Water Flow rate of coolant (L/min) 5.0

As shown in FIG. 36, a contact area of the liquid cooling jacket J4 and the coolant becomes larger as the groove width W1 of the second flow passage B3 a becomes smaller. Therefore, the thermal resistance of the liquid cooling jacket J4 also becomes smaller as the groove width W1 of the second flow passage B3 a becomes smaller. When the groove width W1 of the second flow passage B3 a becomes larger than 1.1 mm, the thermal resistance exceeds 0.08 (degree/W), which is the target thermal resistance.

The pressure loss the coolant is subjected to becomes larger than 5 (Pa) when the groove width W1 of the second flow passage B3 a becomes smaller than 0.2 mm.

Thus, the groove width W1 of the second flow passage B3 a is preferably within the range of 0.2 to 1.1 mm.

Example 2 Analysis of a Relationship Between the Thickness T1 of the Fin 25 b and the Groove Width W1

Similar to the example 1, the groove width W1 of the second flow passage B3 a is set to be 0.2 mm, 0.5 mm, and 1.0 mm (see Table 1). Then, the thickness T1 of the fins 25 b is changed as appropriate in each of the groove with W1 of the second flow passage B3 a. Thus, a relationship between “a ratio between the thickness T1 of the fins 25 b and the groove with W1 (T1/W1)” and “the thermal resistance” is analyzed.

As shown in FIG. 37, there is a range of T1/W1 in which the thermal resistance becomes small in each groove width W1. Within the range, the thermal resistance is smaller than or equal to 105% of the minimum thermal resistance in each groove width W1.

To be more specific, when the groove width W1 of the second flow passage B3 a is 1.0 mm, the minimum thermal resistance is 0.0073 (degree/W), and thus, 105% of the minimum thermal resistance is 0.0076 (degree/W). The range in which the thermal resistance is smaller than or equal to 0.0076 (degree/W) is 0.5≦T1/W1≦1.4.

Similar to this, when the groove width W1 of the second flow passage B3 a is 0.5 mm, the range is 0.7≦T1/W1≦2.1. When the groove width W1 of the second flow passage B3 a is 0.2 mm, the range is 0.8≦T1/W1≦2.9.

A graph shown in FIG. 38 is obtained when “the groove width W1” is represented by the x axis and “the fin thickness T1/the groove width W1” is represented by the y axis on the basis of the analysis above. As shown in FIG. 38, it is verified that “the groove width W1” and “the fin thickness T1/the groove width W1” preferably satisfy the Formula 1.

−0.375×W1+0.875≦T1/W1≦−1.875×W1+3.275  Formula 1

Example 3 Analysis of a Relationship Between the Groove Width W1 of the Second Flow Passage B3 a and the Depth D1 Thereof

In the liquid cooling jacket J4 according to the fourth embodiment, the groove width W1 of the second flow passage B3 a is set to be 0.2 mm, 0.5 mm, and 1.0 mm (see Table 1). Then, the depth D1 of the fins 25 b is changed as appropriate in each of the groove with W1 of the second flow passage B3 a. Thus, a relationship between “the depth D1” and “the thermal resistance” is analyzed.

As shown in FIG. 39, similar to the example 2, it is verified that there is a range of the depth D1 in which the thermal resistance is small. The ranges are calculated similarly to the example 2. When the groove width W1 of the second flow passage B3 a is 0.2 mm, the range is 2≦D1≦6. When the groove width W1 of the second flow passage B3 a is 0.5 mm, the range is 4≦D1≦11. When the groove width W1 of the second flow passage B3 a is 1.0 mm, the range is 6≦D1≦18.

A graph shown in FIG. 40 is obtained when “the groove width W1” is represented by the x axis and “the depth D1” is represented by the y axis on the basis of the analysis above. As shown in FIG. 40, it is verified that “the groove width W1” and “the depth D1” preferably satisfy Formula 2.

5×W+1≦D≦−16.25×W+2.75  Formula 2

Example 4 Analysis of an Efficacy of the Jig

An efficacy of the jig 210 holding the peripheral wall 12 of the jacket body 10 in the friction stir welding of the jacket body 10 and the lid body 31 according to the fourth embodiment is analyzed. In this analysis, two types of the tools 200 shown in Table 3 are used. As shown in Table 4, a length L6 between outer surfaces of shoulders 202 of tool A and tool B and the outer surface of the peripheral wall 12 of the jacket body 10 is changed (see FIG. 19). Then, the peripheral wall 12 and the lid body 31 are friction stir welded with or without the jig 210. The quality of the connected portion is evaluated visually. ◯ indicates a good connection, and x indicates a bad connection in the following tables.

The number of revolutions of the tools 200 is 6000 rpm, and a connection speed is 200 mm/min. A thickness T11 of the peripheral wall 12 is 4 mm (see FIG. 19).

TABLE 3 Tool A Tool B Diameter of shoulder (mm) 6.0 8.0 Diameter of pin (mm) 2.5 3.0 Length of pin (mm) 2.0 2.0

TABLE 4 Quality of connection Tool Length L6 (mm) Jig portion Tool A 1.0 Employed ∘ Tool A 0.5 Employed ∘ Tool B 0.0 Employed x Tool A 1.0 Not employed x

As shown in Table 4, it is verified that the lid body 31 can be connected in good quality without changing the peripheral wall 12 in shape when the jig 210 is employed, even if the peripheral wall 12 is thin and the length L6 is 0.5 mm.

Example 5 A Relationship Between a Pin Length L5 and a Thickness T2 of the Lid Body 31

A relationship between a length of a pin 201 of the tool 200 and a thickness T2 of the lid body 31 is analyzed. As shown in Table 5, the length L5 of the pin 201 is a constant value of 2.0 mm and the thickness T2 of the lid body 31 is changed in this analysis. Then, the quality of the connection portion is visually evaluated.

TABLE 5 Quality of Length L5 of Thickness T2 of connection pin (mm) the lid body (mm) L5/T2 (%) portion 2.0 6.0 33.3 ∘ 2.0 5.0 40.0 ∘ 2.0 4.0 50.0 ∘ 2.0 3.0 66.6 x

As shown in Table 5, it is verified that the peripheral wall 12 and the lid body 31 can be connected in good quality within the range in which the length L5 of the pin 201 is smaller than or equal to 60.0% of the thickness T2 of the lid body 31, which is a member to be connected. 

1. A liquid cooling jacket for transmitting heat generated by a heating element which is installed to a predetermined position to a heat transmission fluid supplied from an external heat transmission fluid supply means and flowing inside of the liquid cooling jacket, the liquid cooling jacket comprising: a first flow passage on a side of the heat transmission fluid supply means; a second flow passage group consisting of a plurality of second flow passages branched from the first flow passage, and a third flow passage installed at downstream side of the plurality of the second flow passages, and collecting the plurality of the second flow passages, wherein the heating element mainly dissipates the heat to the second flow passage group.
 2. A liquid cooling jacket for transmitting heat generated by a heating element which is installed to a predetermined position to a heat transmission fluid supplied from an external heat transmission fluid supply means and flowing inside of the liquid cooling jacket, the liquid cooling jacket comprising: a first flow passage, a plurality of a second flow passage groups each of which consists of a plurality of second flow passages, and a third flow passage toward downstream in order, wherein the heating element mainly dissipates the heat to the second flow passage groups, and the adjacent second flow passage groups are connected in series via a communication flow passage.
 3. The liquid cooling jacket according to claim 2, wherein the adjacent second flow passage groups are disposed side by side, and a lower end of one of the adjacent second flow passage groups and an upper end of the other one of the adjacent second flow passage groups are on the same side.
 4. The liquid cooling jacket according to claim 1, comprising a tube bundle formed by bundling a plurality of metallic tubes, wherein an inner hole of each of the plurality of metallic tubes is the second flow passage.
 5. The liquid cooling jacket according to claim 1, further comprising a metallic tube having a plurality of inner holes, wherein each of the inner holes is the second flow passage.
 6. The liquid cooling jacket according to claim 1, further comprising a plurality of metallic fins arranged at a predetermined interval, wherein a space between the adjacent fins is the second flow passage.
 7. The liquid cooling jacket according to claim 6, wherein a width W of the second flow passage is in the range of 0.2 to 1.1 mm.
 8. The liquid cooling jacket according to claim 6, wherein the width W of the second flow passage and a thickness T of the fins disposed between the adjacent second flow passages satisfy Formula
 1. −0.375×W+0.875≦T/W≦−1.875×W+3.275  Formula 1
 9. The liquid cooling jacket according to claim 6, wherein a depth D of the second flow passage and the width W of the second flow passage satisfy Formula
 2. 5×W+1≦D≦−16.25×W+2.75  Formula 2
 10. The liquid cooling jacket according to claim 6, further comprising: a fin member comprising the plurality of metallic fins and a base from which the plurality of metallic fins are extended; a jacket body for housing the fin member, wherein the base is heat-exchangeably fixed to the jacket body.
 11. The liquid cooling jacket according to claim 6, further comprising: a first fin member comprising a first base and a plurality of first fins extended from the first base; a second fin member comprising a second base and a plurality of second fins extended from the second base, wherein the first fin member and the second fin member are combined such that the plurality of the first fins and the plurality of the second fins are interlocked together, the plurality of metallic fins are composed of the first fins and the second fins, and the second flow passage is formed between the first fin and the second fin adjacent to each other.
 12. The liquid cooling jacket according to claim 11, wherein the heating element is installed on a side of the first base, a protruding length of the first fin is set to be equal to or shorter than a protruding length of the second fin, and the plurality of the second fins is thermally connected to the first base.
 13. The liquid cooling jacket according to claim 6, further comprising: a jacket body comprising a fin housing for housing the plurality of the metallic fins; a sealing member for sealing the fin housing; wherein a contact area where a peripheral wall of the jacket body surrounding the fin housing and the sealing member are in contact with each other is friction stir welded, and a start end of the area which is friction stir welded overlaps with a finish end of the area which is friction stir welded.
 14. The liquid cooling jacket according to claim 13, wherein the plurality of metallic fins is extended from the sealing member and integrally formed with the sealing member.
 15. The liquid cooling jacket according to claim 13, wherein the peripheral wall is friction stir welded with a jig holding the peripheral wall so that the peripheral wall does not protrude outward.
 16. The liquid cooling jacket according to claim 13, wherein a length of a pin of a tool to be used in the friction stir welding is less than or equal to 60% of a thickness of the sealing member.
 17. The liquid cooling jacket according to claim 13, wherein a position where the tool is pulled apart does not overlap with the contact area in the friction stir welding.
 18. The liquid cooling jacket according to claim 1, further comprising a metallic honeycomb member comprising a plurality of minute holes, wherein each of the plurality of minute holes is the second flow passage.
 19. The liquid cooling jacket according to claim 1, further comprising: a ripple cross-section metallic heat dissipating sheet, and a metallic jacket body to which the heat dissipating sheet is heat-exchangeably fixed, wherein the second flow passage is formed between the heat dissipating sheet and the jacket body.
 20. The liquid cooling jacket according to claim 6, wherein the metal is aluminum or aluminum alloy.
 21. The liquid cooling jacket according to claim 1, wherein a heat transmission fluid inlet communicating with the first flow passage and a heat transmission fluid outlet communicating with the third passage are arranged symmetric with respect to the heating element.
 22. The liquid cooling jacket according to claim 21, wherein the inlet and the outlet are arranged relatively away from each other.
 23. The liquid cooling jacket according to claim 21, wherein the inlet and the outlet are arranged such that the inlet and the outlet come closer to the heating element.
 24. The liquid cooling jacket according to claim 1, wherein the heating element is a CPU. 